The applicant of the present patent application has proposed, in the Japanese Utility Model Application No. 57-172593, Connector Socket, a connector socket having the excellent characteristics that it exhibits a strong engaging force to the plug although small in size and does not easily release the plug, the plug inserting position can be found easily, and on the occasion of inserting the plug the male contacts of the plug are prevented from being placed in contact with female contacts in the incorrect positions.
The characteristic structure of the connector socket proposed previously and the effects obtained from that structure are outlined hereinafter in reference to FIGS. 1 to 3.
The connector socket in question has a structure in which an annular recessed groove 2 is formed, as shown in FIG. 1, at one end surface (front surface) of an insulation body 1 to/from which the plug is inserted or removed, and a cylindrical annular contact 3 as shown in FIG. 2 is engaged with the annular recessed groove 2.
A plurality of female contact accommodating holes 5 are formed in a cylindrical portion of the insulation body 1 surrounded by the annular recessed groove 2. In this example, five female contact accommodating holes 5 are formed. The structure explained up to this step is similar to that of a connector socket which is generally called the DIN type connector.
The first feature of this connector socket is that in spite of being small in size it ensures a strong engaging force to a plug owing to a structure in which orthogonally crossing diameters L.sub.1 and L.sub.2 of the annular contact 3 are selected to be L.sub.1 &gt;L.sub.2 as shown in FIG. 2 to form a cylindrical ellipse.
Where the annular contact 3 is formed as such a cylindrical ellipse, a sufficiently strong engaging force to a cylindrical metal cover 6 of plug 50 can be obtained when the plug 50 shown in FIG. 3 is inserted into the connector socket. Accordingly, a strong engaging force can be obtained even when the engaging area of the cylindrical metal cover 6 of the plug 50 is narrowed due to reduction in size of the plug. As a result, even if a pulling force is applied to a cable 51 connected to the plug 50, the plug 50 will not easily fall out of the socket.
It is the second feature of the connector socket shown in FIG. 1 that auxiliary recessed grooves 8A, 8B are formed, in addition to a main recessed groove 7 for positioning, in the circumference of a cylindrical column portion 4 surrounded by the annular recessed groove 2 as shown in FIG. 1.
Corresponding respectively to the main recessed groove 7 for positioning and auxiliary recessed grooves 8A and 8B, a main protrusion 9 for positioning and auxiliary protrusions 11A, 11B are formed to the internal surface of the cylindrical metal cover 6 of the plug 50 as shown in FIG. 3. The inserting positions are prevented from being confused by making the main protrusion 9 different in size from the auxiliary protrusions 11A, 11B. Since three recessed grooves 7, 8A and 8B and three protrusions 9, 11A and 11B are provided, if the plug and socket are not in a correct engaging position with respect to each other when an attempt is made to insert the plug 50 into the socket, the three protrusions 9, 11A and 11B abut the circular edge of the cylindrical column portion 4 surrounded by the annular recessed groove 2, thereby positioning the axial center of plug 50 in agreement with the axial center of socket. Therefore, while such condition is maintained, the plug 50 can easily be rotated about the axial center of socket to find the correct engaging position.
It is the third feature of the connector socket of FIG. 1 that a square hole 12 is formed in the cylindrical column portion 4 surrounded by the annular recessed groove 2 as shown in FIG. 1. This square hole 12 is engaged with an insulated square column 13 (in FIG. 3) provided in the plug 50 and this engagement also defines the correct engaging position between the plug and socket. This insulated square column 13 is formed a little longer than contact pins 14 of the plug 50. Owing to this structure, it is only when the insulated square column 13 enters the square hole 12 the socket that insertion of the contact pins 14 of the plug 50 to the female contact accommodation holes 5 can be allowed. As a result, there is no chance for the contact pins 14 of plug 50 to enter wrong female contact accommodating holes 5 of the socket.
As explained above, the connector socket proposed previously results in the effects that a strong engaging force to the plug can be ensured even with a smallsized socket, a plug inserting position can be found easily, and incorrect connection will never occur.
However, a small-sized connector socket of the type described above has a structure which cannot be mounted directly on a printed circuit substrate because terminals for the female contacts are led out from the rear surface opposite to the plug inserting and removing surface.
Moreover, since the annular contact 3 does not perfectly cover the female contact up to the rear end side, sufficient shielding function by the annular contact 3 cannot be obtained. Therefore, if this connector socket is used for connection with a personal computer, for example, various disadvantages may occur, namely, external noise can enter via said connector socket and destroy data in the computer, and the signals sent or received through this connector socket may be sent therethrough to the outside.